1. Technical Field of the Invention
This invention relates to control systems and methods for controlling inverter based electrical power generation and feeding of generated power to a grid. This invention particularly relates to an integrated control system and method that integrates a variety of power control functions including state machine control of distinct operational modes, synronization with the grid, power factor control and utility outage ride-through.
2. Description of Related Art
Various control devices for controlling inverter based electrical power generation are known in the art. Typical controllers utilize analog voltage or current reference signals, synchronized with the grid to control the generated wave form being fed to the grid. Such controllers, however, lack distinct control states and the capability of controlling transitions between specifically defined control states.
Various techniques for synchronizing the frequency of generated power to the frequency of a grid are also known in the art. Such conventional line synchronizers typically sense the line frequency of the grid and lock to the grid when the generated frequency drifts into synchronization.
Such conventional line synchronizers, however, do not have the ability to control the rate of phase shift of the generated power or the ability to interface easily with both 50 Hz and 60 Hz grids.
Various techniques for controlling the power factor are also known in the art. In the context of electrical power generation, for example, Erdman, U.S. Pat. No. 5,225,712, issued Jul. 6, 1993, discloses a variable wind speed turbine electrical power generator having power factor control. The inverter can control reactive power output as a power factor angle or directly as a number of VARs independent of the real power. To control the reactive power, Erdman utilizes a voltage waveform as a reference to form a current control waveform for each output phase. The current control waveform for each phase is applied to a current regulator which regulates the drive current that controls the currents for each phase of the inverter.
Although the conventional art may individually provide some of these features, the combination of these features particularly when utilized in conjunction with an integrated system utilizing state machine control is not found in the art.
Other applications distinct from electrical power generation also utilize power factor control devices. For example, Hall, U.S. Pat. No. 5,773,955 issued Jun. 30, 1998, discloses a battery charger apparatus that controls the power factor by vector control techniques. The control loop utilized by Hall controls power delivery to the battery to obtain a desired charge profile by individually controlling the real and reactive components of the AC input current. The AC input current is forced to follow a reference that is generated in response to information received by the battery charge control circuit to supply the desired charging current to and remove discharge current from a battery.